1. Field of the Invention
The present invention relates to a fixing apparatus which is used in an image forming apparatus adopting the electrophotographic system, electrostatic recording system or the like, such as a printer or a copying machine, and which serves to fix an unfixed image on a recording material.
2. Related Art
Conventionally, with regard to an image forming apparatus adopting the electrophotographic system, electrostatic recording system or the like, such as a printer or a copying machine, a fixing apparatus using a heat roller is known as means for fixing an unfixed image on a recording material to the recording material. Such a fixing apparatus has a problem in that it involves large power consumption and that the time required for attaining a temperature at which fixing is possible, that is, the so-called warming-up time, is rather long.
As disclosed in Japanese Patent Application Laid-open No. 63-313182, to overcome the above problems, a fixing apparatus adopting a film fixing system using a heat resisting film has been proposed and put into practical use.
A fixing apparatus adopting the film fixing system is equipped, for example, with a thin and heat resisting rotatable fixing film constituting a film member, a driving roller for rotating the fixing film, a heating member serving as heating means secured in position so as to be in slide contact with the inner peripheral surface of the fixing film, and a pressurizing roller serving as a pressurizing member arranged so as to be held in press contact with the heating member through the intermediation of the fixing film.
The fixing film and the pressurizing roller are rotated at a peripheral velocity which is the same as the recording material conveying speed at least during execution of image fixing processing. By conveying the recording material while pinching it by a fixing nip portion serving as a nip region formed by bringing the pressurizing roller into press contact with the heating member through the intermediation of the fixing film, heat energy of the heating member and pressure from the pressurizing roller are imparted to the visual image on the recording material to soften and fuse the visual image. Further, by discharging the recording material from the fixing nip portion, the visual image is cooled and solidified to be fixed to the recording material.
In a fixing apparatus adopting such a film fixing system, a member like a small diameter aluminum roller (removing member) is brought into contact with the pressurizing roller, whereby residual toner on the pressurizing roller is removed, and staining of the recording material due to staining of the pressurizing roller, jam in which the recording material is entangled with the pressurizing roller, etc. are prevented.
As compared with cleaning means like a web which is arranged so as to be in contact with the fixing roller or the pressurizing roller, the above-mentioned removing member like the aluminum roller leads to a lower cost, so that it is partly adopted in a fixing apparatus adopting the heat roller system.
Residual toner adhering to the surface of the pressurizing roller is once fused and softened at the contact nip position between the pressurizing roller and the removing member, and, immediately after passing the contact nip position, is cooled and solidified on the removing portion, whereby it is removed from the pressurizing roller.
However, in the removing member consisting of an aluminum roller or the like of the above conventional fixing apparatus, toner is not sufficiently fused and softened in the contact nip portion between the pressurizing roller and the removing member if the metal roller is not warmed to a sufficient degree, resulting in poor cleaning performance. Thus, in the fixing system using the heat resisting film which needs no warming up, the metal roller is not suitable. Thus, the residual toner that cannot be collected by the removing member consisting of a metal roller returns to the pressurizing roller to thereby stain the recording material.
Also in the fixing apparatus adopting the heat roller system, in particular, when a thin-walled heat roller whose core thickness is not more than 1 mm is used, the control temperature of the fixing nip portion at standby is kept low and transition to sleep mode occurs in a short time. Thus, the temperature of the pressurizing roller is too low and the metal roller is hard to warm itself up, leading to the same problem as that of the system using the heat resisting film.
In view of this, in a conventionally known system, each time fixing operation is performed on a predetermined number of sheets, the pressurizing roller is rotated to heat the pressurizing roller surface and the cleaning roller by the heating member to thereby fuse and soften the toner, thereby achieving a cleaning effect.
However, to achieve a cleaning effect to solve the above problem, the cleaning process has normally to be performed for approximately 90 seconds, and the next image forming operation cannot be performed during cleaning and there is an increase in power consumption during cleaning.
It is an object of the present invention to provide a fixing apparatus capable of cleaning a fixing rotating member.
Another object of the present invention is to provide a fixing apparatus which allows switching of the speed of the fixing rotating member between fixation mode and cleaning mode.
Still another object of the present invention is to provide a fixing apparatus comprising: a fixing rotating member for pinching and conveying a recording material supporting an unfixed image to perform fixation; driving means for driving the fixing rotating member; a cleaning rotating member for cleaning the fixing rotating member; and contact/separation means for bringing the cleaning rotating member into contact with and away from the fixing rotating member, wherein the driving means drives the fixing rotating member at a predetermined fixing speed during fixation and at a cleaning speed lower than the fixing speed during cleaning by the cleaning rotating member.
Further object of the present invention will become apparent from the following description.